The bovine industry is highly specialized and dairy cattle have been bred to efficiently produce large volumes of milk. The United States dairy herd produced 83.9 billion kg (185 billion lbs.) of milk in 2007, up from 52.6 billion kg (116 billion lbs.) in 1950, yet there are only about 9 million cows on U.S. dairy farms—about 13 million fewer than in 1950.